Datasheet

bq500410A

SLUSB96 – NOVEMBER 2012

www.ti.com

Parasitic Metal Object Detect (PMOD) and Foreign Object Detection (FOD)

The bq500410A is WPC1.1 ready and supports both enhanced PMOD and FOD features by continuously

monitoring the input voltage and current to calculate input power. Combining input power, known losses, and the

value of power reported by the RX device being charged, the bq500410A can estimate how much power is

unaccounted for and presumed lost due to metal objects placed in the wireless power transfer path. If this

unexpected loss exceeds the threshold set by the LOSS_THR resistor, a fault is indicated and power transfer is

halted. Whether the PMOD or the FOD algorithm is used is determined by the ID packet of the receiver being

charged.

PMOD has certain inherent weaknesses as rectified power is not ensured to be accurate per WPC1.0

Specification. The user has the flexibility to adjust the LOSS_THR resistor or to disable PMOD by leaving pin 43

open should issues with compliance or interoperability arise.

The FOD algorithm uses information from an in-system characterized and WPC1.1 certified RX and it is therefore

more accurate. Where the WPC1.0 specification requires merely the Rectified Power packet, the WPC1.1

specification additionally uses the Received Power packet which more accurately tracks power used by the

receiver.

As default, PMOD and FOD share the same LOSS_THR setting resistor for which the recommended starting

point is 400 mW (selected by a 56.2-kΩ resistor on the LOSS_THR option pin 43). If, for some reason, the

application requires disabling one or the other or setting separate PMOD and FOD thresholds, Figure 5 can be

used.

Resistor R39 sets the FOD threshold and R24 sets the PMOD threshold in this configuration. The control lines

(FOD and PMOD) are driven briefly at power-up when the resistor values are read.

To selectively disable PMOD support, R24 and Q8-B should be omitted from the above design.

Product Folder Links: bq500410A